A typical lead frame is a metallic strip, approximately 1".times.9", onto which about 10 to 15 semiconductor microcircuit chips are bonded. After bonding, the chips must be encapsulated with a suitable thermosetting epoxy material, for example, which completely encapsulates each chip, and necessarily a small portion of the lead frame onto which the chips are bonded. Typically, the lead frames with microcircuit chips bonded thereto, will be inserted into a molding press and encapsulated with the thermosetting material by the process known as transfer molding. After each chip of the lead frame is individually encapsulated, each encapsulated chip will be separated from the lead frame into a discrete device for subsequent use in electronic applications of diverse nature.
The practice commonly employed in the industry is to manually load the lead frames onto a loading frame positioned atop a heating plate. The loading frames are subsequently positioned in an encapsulation mold for encapsulation of the chips.
The present invention provides a machine which automatically rapidly loads lead frames with the chips already bonded thereto onto loading plates or frames for encapsulation of the chips.
The lead frames, complete with bonded microcircuit chips, are supplied in magazine type containers by the various electronic companies for encapsulation of the chips. The companies prefer using magazines of their own design or choice but typically include slotted storage racks capable of containing a lead frame on each of the 10 to 50 or more racks. The magazine serves to protect the vertically stacked lead frames with their microcircuit chips delicately soldered thereto. The lead frames stacked within the magazines are automatically individually removed therefrom and ultimately automatically loaded in precise position onto the loading frames.
Briefly, the present invention includes an air cylinder having a piston which causes a plurality of parallel connected pusher blades to each eject a lead frame from a separate magazine wherein a row of such magazines, equal in number to the pusher blades, is horizontally disposed. The lead frames are ejected onto a nest member which pivots 180.degree. to deposit the lead frames onto the loading frame. The lead frames are precisely positioned on the pivoting nest member during uninterrupted rotation thereof. More specifically, after about 45.degree. of rotation of the nest member, the lead frames slide downwardly on the smooth surfaced nest member a short distance to contact an abutment; and vacuum means applied to the nest member immediately after contact maintains the lead frames in a precise position on the nest member, i.e., in contact with the abutment, until deposited onto the loading frame upon completion of its 180.degree. rotation. The loading frame may then be automatically rotated in order to accept another set of lead frames on its remaining half prior to being replaced by an empty loading frame.